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Double Galvanized Steel Strand 

and 

Iron Wire 

for 

Electrical Transmission 

and 

Distribution 



Indiana Steel and Wire Company 

Mimcie, Indiana, U. S. A. 



uigitizeci by 



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CttLEBE 



Copyright 1921 
Indiana Steel and Wibb Company 



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PREFACE 



There has been widespread inquiry for information 
concerning the use of double galvanized iron wire and 
steel strand for transmission purposes. 

The mechanical properties of iron wire and steel 
strand are well known but their electrical characteris- 
tics under various conditions have not received as much 
investigation. 

Recognizing this fact, we have had prepared and are 
submitting herewith a technical report covering tests 
made on steel strand and iron wire to determine their 
electrical characteristics for power conductors. 

It contains new data and information which we be- 
lieve the Engineering Profession will welcome, and will 
find useful and helpful in considering the use of steel 
power conductors. 

There are many cases where iron wire and strand can 
be, and are being successfully used in power lines, with 
reliability and economy. 

Just when and how depends on local conditions and 
is purely an engineering problem but the following treat- 
ise should aid you materially in solving your own indi- 
vidual problems. 

This booklet covers in a general way the very points 
that have been uppermost in the minds of Engineers 
and should fill a real want in the field of Transmission 
Line Engineering. 

Indiana Steel and Wire Company 



March 1, 1921 

uigitizedby VjOOyli:^ 



TABLE OF CONTENTS 



Double Galvanized Steel Strand and Iron Wire for 

Electrical Transmission and Distribution: page 

Purpose of Tests 7 

Test Samples 7 

Data on Samples Tested 8 

Results Sought 9 

Test Methods 9-11 

Properties with Continuous Currents: 

Resistivity 11 

Resistance 11 

Temperature Coefficient 11 

Table, Properties with Continuous Currents 12 

Variations in Resistivity 13 

Properties with Sine-Wave Alternating Currents: 

Skin-Eflfect 13-14 

Formulas For Inductance 15-16 

Internal Inductance Ratio 16 

Power Losses 16 

Tabular Summary of Results 16-17 

Tables, f-in. High Strength Steel Strand 18 

Tables, J-in. Siemens-Martin Steel Strand 19 

Tables, |-in. Siemens-Martin Steel Strand 20 

Tables, }-in. Siemens-Martin Steel Strand 21 

Tables, f-in. Standard Steel Strand 22 

Tables, 3-Ply No. 8 B. W. G. Twisted Guy Wire 23 

Tables, No. 6 B. W. G. "B. B." Telephone and Tele- 
graph Wire 24 

Temperature Rise 25 

Table, Temperature Rise Above Air Temperature ... 25 
Curves of Effective Resistance and Internal 

Reactance 25-26 

Tables of Effective Resistance, Internal Reactance 

and Line Loss 26 

Comparison op Results: 

Comparisons Among Three Different Grades of 

Strand of Equid Size 26 

Table, Comparisons Among Three Different Grades 

of l-in. Steel Strand 26-27 

Table, Effective (A.C.) Resistance of f-in. Steel 

Strand— Ohms Per Mile 27 

Comparisons Among Three Different Sizes of Sie- 
mens-Martin Strand 28 



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TABLE OP CONTENTS 



Comparison op RESULTSi-^Jontinned. page 

Comparisons Among Standard Strand, Guy Wire 

and '*B. B." Wire 28-30 

Table, Comparisons Among Standard Strand, Guy 

Wire and "B. B." Wire 29 

Wave Distortion 30-31 

COBfMERCIAL APPUCATION: 

Line Resistance, Reactance and Impedance 31-32 

Line Drop and Loss 32 

Current Carrying Capacity 32 

Example of Appucability of Steel Cable to High 

Tension Transmission 32-33 

Second Example 33-34 

Example of Applicability to Short Lines Carrying 

Small Loads 34-35 

Relative Costs 35 

Conclusions 35-36 

Appendix A. Curves op Eppectivb Resistance and 
Internal Inductance: 

Diagrams 39-41-43-4&-47-49-51 

Appendix B. Tables op Effective Resistance, Inter- 
nal Reactance and Line Loss: 

f-in. High Strength Strand 55 

i-in. Siemens-Martin Strand 55 

f-in. Siemens-Martin Strand 56 

J-in. Siemens-Martin Strand 56 

f-in. Standard Strand 57 

3-Ply No. 8 Twisted Guy Wire 57 

No. 6 B. B. Telegraph Wire 58 

Appendix C. Telephone Transmission Equivalents op 
Iron Wire: 

Table 61 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind. 



DOUBLE GALVANIZED STEEL STRAND 

AND 

IRON WIRE 

FOR 

ELECTRICAL TRANSMISSION 

AND 

DISTRIBUTION 

INDIANA STEEL AND WIRE COMPANY 
MUNCIE, INDIANA, U. S. A. 



Purpose of Tests. The object of these tests was to 



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determine the electrical properties of certain represen- 
tative sizes and grades of steel strand and iron wire, 
with continuous currents and with sine-wave alterna- 
ting currents, xinder a range of conditions such that the 
results would be applicable in designing transmission 
and distribution lines in which steel conductors might 
be employed with advantage. The results of the tests 
are therefore presented and siunmarized in form in- 
tended to furnish convenient design data. 

Test Samples. The following table shows sizes and 
grades of galvanized steel conductors selected for test; 
samples were chosen and submitted by the Indiana Steel 
and Wire Company. 



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Results Sought The tests were arranged to deter- 
mine the following properties of the samples submitted. 

1. Continuous-current resistance and resistivity. 

2. Temperature coefficient of resistance. 

3. Alternating-current resistance at 25 and 60 cycles. 

4. Alternating-current inductance at 25 and 60 cycles. 

Test Methods. The tests were conducted at the Elec- 
trical Testing Laboratories of New York City and are 
described in detail in their report No. 24,439 rendered 
to the undersigned, copy of which is submitted herewith. 
The following brief description is extracted from their 
report. 

"The object of the test was to determine the alter- 
nating current resistance and the internal inductance of 
the various samples of wire when traversed by sine- 
wave alternating current at frequencies of 25 and 60 
cycles per second. The temperature rise of the wires 
under these conditions was noted. Measiu'ements were 
also made of the resistivity and the resistance tempera- 
ture coefficient. 

"Briefly stated, the alternating current measure- 
ments were made by a Wheatstone bridge method, the 
wire being suspended in air in the form of a long nar- 
row rectangular loop of constant and known dimensions. 
The resistance and total inductance of this loop were 
determined in terms of known standard resistors and 
inductors. 

"The average length of the test loops was approx- 
imately 115 feet and the width 30 inches, the wire be- 
ing supported in a horizontal plane by means of wooden 
spacers with "V" notches to give constant spacing. 
The loop was broken at the center for the introauction 
of current, the ends of the wire dipping in pools of 
mercury which were connected to the bridge net work. 

"In all measurements, four observations of induc- 
tance and two of resistance were made, the inductance 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind, 



being observed with direct and reversed current in the 
bridge and with direct and reversed current, for each 
of these two conditions, through the inductance. . . . 
Provision was also made to throw the testing circuit on 
to direct current immediately upon the completion of 

the observations with alternating current The 

various values of alternating current were maintained 
imtil the resistance of the loop had attained final value. 
.... The measurements with alternating current 
were all made with current having a sine wave shape. . 

"In order to check the accuracy of the results ob- 
tained, a loop composed of No. 8 copper wire was strung 
and measured in the same manner as the iron wire loops. 
The measured value of inductance obtained in this meas- 
urement showed satisfactory agreement with that ob- 
tained by computation, indicating that correct results 
had been obtained in inductance measurements. The 
measured a.c. resistance of this copper loop was identi- 
cal with its measured d. c. resistance, indicating that 
there were no additional power losses in neighboring 
floor beams, columns, etc. 

"In making the resistivity and resistance tempera- 
ture coefficient determinations, a wire from each of the 
seven samples was stretched in a bath of oil, the tem- 
perature of which could be readily varied. The resis- 
tance of known lengths of these specimens were meas- 
ured at various temperatures and from these values 
and the diameter of the wire, both resistivity and resis- 
tance temperature coefficients were computed. 

"In making the computations, the observed data 
were first corrected for the resistance and inductance 
of the copper leads. The corrected loop resistance was 
then adjusted for the difference between the observed 
air temperature and 20 degrees C, using the resistance 
temperature coefficient obtained in the measurement de- 
scribed above. The external inductance of each of the 
loops was then computed from the measured dimensions 
of the wire and the loop, using the standard equation 
for the inductance of a rectangle taking care to exclude 



10 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind, 



the expression representing the internal inductance of a 
non-magnetic wire (Bureau of Standards, Vol. VIII., 
No. 1, p. 155). The difference between this value and 
the measured inductance gave the internal inductance 
of the sample." 



Properties with Contifltioos Currents 

Resistivity. The values of resistivity given in the 
following table are stated in microhm-inch (millionths of 
an ohm between opposite parallel faces of a one-inch 
cube) and in ohms per mil-foot (round wire one foot 
long and one mil in diameter) at 20 degrees Centi^ade. 
For convenience the ratios of the several resistivities to 
the International Annealed Copper Standard are also 
stated, and the ratios of the conductivities. 

Resistance. The resistances of the several conduc- 
tors are stated in the table in ohms per 1,000 ft. 
and per mile at 20 degrees Centigrade. These values 
are computed values based on the measured resistivity 
and cross-section of each sample. 

Temperature Coefficient. The values for the temper- 
atiu'e coefficient given in the table (following) express the 
change in resistance per degree Centigrade, from and at 
a reference temperature of 20 degrees Centigrade (68 
degrees Fahrenheit). The values of the coefficient were 
computed from observed values of resistance at 20 de- 
grees and 90 degrees Centigrade. 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



Variations in Resistivity. With such metals as com- 
mercially pure copper and aluminum, in which all 
foreign elements or impurities can be reduced to a 
small fraction of one per cent, it is possible to standard- 
ize values of electrical resistivity with high precision, 
but with commercial iron and steel the case is dif- 
ferent. The latter metals, by reason of a higher pro- 
portion of impurities due to less refined methods of 
manufacture and also, in the case of steel, by reason of 
certain proportions of other elements such as carbon, 
manganese, silicon, etc., are necessarily more complex 
in structure and imder less perfect control as to com- 
position. Hence the electrical resistivity of commercial 
grades of iron and steel wire should be stated in terms 
of averages, with certain maximum values or toler- 
ance limits within which all (or all but a few per cent) 
of the material of a specified quality should conform. 

The foregoing values of resistance (given in the table 
just preceding) check reasonably well with the measured 
resistance with continuous current (5 amp.) of each 
full sample of strand, as given later, the average dif- 
ference being 2.2% with a minimimi of zero and a 
maximum of 6.7%. These dijfferences do not seem to 
be abnormal. 

Properties with Sioe-Waye Attematiog Cmreats 

Skin-Effect. The effective resistance of a conductor 
when traversed by an alternating current is greater than 
the ohmic or real resistance with continuous current, 
the ratio of the former to the latter being termed the 
skin-effect resistance ratio. Simultaneously with in- 
crease of resistance with alternating currents, there is 
a decrease of internal inductance, or that portion of 
the total inductance of the circuit which corresponds 
to the magnetic flux within the substance of the con- 
ductor; the ratio of the effective alternating-current 
internal inductance to the true internal inductance is 
termed the skin-effect inductance ratio. The magni- 
tude of the skin-effect depends upon the following 



13 Digitized by LjOOQIC 



INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



factors: size of conductor, contour of cross-section, 
character of lay if stranded, resistivity, frequency and 
wave form of the current and magnetic properties of 
the conductor material. 

Primarily the cause of skin-effect is the lack of full 
penetration of the current throughout the cross-section 
of the conductor, being least, in the case of circular 
cross-section, at the center and maximum at the cir- 
cumference. Lack of full penetration occurs because 
the internal reactance of the conductor is not uniform 
over its entire cross-section, but ranges from maximum 
at the center to minimum at the circumference, as the 
result of corresponding variation in the inductance. In 
general the skin-effect becomes greater with increasing 
diameter of conductor and with increasing frequency, 
but decreases with increasing resistivity. With mag- 
netic materials having high permeability it is also much 
larger than with materials of low permeabiUty or with 
non-ferrous materials having substantially unit per- 
meability. 

Wires of iron and steel, besides possessing magnetic 
permeability in varying degree, are subject to hystere- 
sis, thus introducing another source of energy loss, not 
as important as the impairment of penetration, but 
contributing its quota to the resultant skin-effect. 
Spiral stranding of the conductor, as in concentric-lay 
or rope-lay cables, introduces still another element of 
loss termed the spirality effect, which is much more 
marked in iron and steel cables than in similar cables of 
non-magnetic materials. 

The resultant skin-effect for non-magnetic power con- 
ductors of the usual types and sizes can be calculated 
or predetermined with rather close precision, but in the 
case of iron and steel conductors this becomes very dif- 
ficult if not impracticable. Experimental results there- 
fore become essential to the establishment of reliable 
design data for iron and steel conductors and are con- 
veniently stated in terms of the skin-effect resistance 
ratio at various frequencies and current densities and 



14 Digitized DyvjOOQ IC 



INDIANA STEEL AND WIRE COMPANY, Muncie, Ind, 



in terms of the ratio of the effective internal inductance 
to the true internal inductance of an identical form of 
conductor having unit permeability. The results oif the 
tests herein reported are expressed in the foregoing 
terms, in addition to stating the effective resistance 
and internal inductance per 1,000 feet and per mile of 
conductor. 

Formulas For Inductance. The following formulas 
express the true inductance of a uniform linear conduc- 
tor, with parallel return, in millihenrys per mile of con- 
ductor. 



(a) Solid round wire: 

L = 0.7411 logio ^ + 0.0805/. (1) 

r 



(b) 3-Ply strand: 

L = 0.7411 logio - + 0.1252m (2) 

r 



(c) 7-Wire strand: 

L = 0.7411 logio - + 0.1033/i (3) 



The symbol d stands for the perpendicular separa- 
tion of the conductor from its parallel return conductor 
(center to center) and r represents the radius of the 
wire or the circumscribing circle of the strand, both 
expressed in the same units. These formulas apply 
when the ratio d/r is large, as in ordinary overhead cir- 
cuits of open wire, but should never be used if d/r is 
small, as in multiple-conductor cables. The logarith- 
mic portion of each formula, which is the same in every 
case, represents the external inductance or that portion 
due to the magnetic flux which is wholly outside of the 
conductor itself. The symbol m stands for the mag- 
netic permeability of the conductor, here assumed for 



15 



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INDIANA STEEL AND WIRE COMPANY, MuncU, Ind, 



simplicity's sake to be constant throughout the cross- 
section and uniform at all current densities, but in reali- 
ty a variable. The constant portion of each formula, 
containing the factor ti, represents the internal induc- 
tance or that portion due to the magnetic flux which is 
wholly inside of the conductor itself. These formulas 
are strictly applicable to non-magnetic conductors of 
imit permeability, such as copper and aluminum, but as 
applied to iron and steel conductors the value of n which 
gives a correct result when substituted in the formula 
is merely an average or equivalent single value which in 
reality is the ratio of the internal inductance of the iron 
or steel conductor to the corresponding inductance of a 
non-magnetic conductor with zero skin-effect. The 
latter significance should be attached to any equiva- 
lent values of fji for iron or steel conductors computed 
from the results of the tests hereafter shown. 

Internal Ind/acUmce Ratio. Since the internal induc- 
tance and reactance of wires and cables having unit 
permeability are readily calculated, it becomes conven- 
ient in the case of iron and steel conductors to have the 
ratio of their effective internal inductance with alter- 
nating currents to the true internal inductance of similar 
conductors having unit permeability. This ratio has 
been computed and stated for each case shown in the 
tabular summary of results which follows. 

Power Losses. The usual expression !%• represent- 
ing the power loss in watts in a conductor of resistance 
r ohms traversed by a current of I amperes will apply 
in the present case, but with continuous currents the 
real or ohmic resistance should be used in the formula, 
whereas with alternating currents the effective or ap- 
parent (A.C.) resistance should be used. 

Tabular Summary of Results. The following tables 
show the results of the tests upon the seven samples be- 
fore mentioned, with continuous current and with sine- 
wave alternating current, at five dijfferent current 
strengths and with frequencies of 25 and 60 cycles. 



16 

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INDIANA STEEL AND WIRE COMPANY, MuncU, Ind. 



Each value of resistance given in the tables corresponds 
to the final temperature which the conductor would 
reach, with the stated value of current, when the air 
temperature is 20 degrees Centigrade; that is to say, 
each value of resistance includes the heating effect in 
the conductor under the condition of an air tempera- 
ture of 20 degrees Centigrade. The temperature nse in 
each instance is stated in a subsequent table. Atten- 
tion is called in particular to the skin-effect resistance 
ratios and the internal inductance ratios. 



J 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 






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21 



uigitizeci by 



INDIANA STEEL AND WIRE COMPANY, Munde, Ind, 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



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23 



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INDIANA STEEL AND WIRE COMPANY, Muneie. Ind. 



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Csi lO 



-^ 00 

a> 00 



00 t* 



1-H 00 00 00 



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1-H U3 lO U3 



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t> o> C^ ^ 
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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind. 


Temperature Rise. In making the tests the various 
values of alternating current were maintained until the 
resistance of the loop had attained final value. The 
observed rise of temperature of each sample above air 
temperature (20 deg. Cent.) is given for each test in the 
accompanjring table. 

Temperatiire Rise AboYe Air Temperatare 

(Deg. Cent.) 




Test 
Frequency 


Current in Amperes | 


5 
0.2 

0.2 

0.2 
0.2 

0.4 
4 

0.6 
0.6 

0.2 
0.2 

0.2 
0.2 

0.2 
0.2 


10 


16 


20 


26 
4.6 

2.8 
3.0 

6 6 
6 4 

17.8 
18.2 

5.0 
5.6 

9.2 

8.6 

22.8 
18.4 


H-in. High Strength Strand 


60 
25 


0.6 
0.8 

0.8 
0.8 

1 4 
1.6 

2.8 
3.2 

1.0 
1.2 

1.0 
1.0 

2.8 
2.6 


1.8 
1.6 

1.2 
1.2 

2 4 

3 

5.4 

7.4 

2.0 
2.0 

2.6 
3.6 

7.4 
6.6 


3.0 

1.8 
1.8 

4 6 
4.4 

11.8 
12.6 

2.6 
3.0 

5.8 
5.4 

13.2 
10.6 


J4-in. Siemens-Martin Strand 


60 
26 


^-in. Siemens-Martin Strand 


60 
25 


Ji-in. Siemens-Martin Strand 


60 
25 


^-in. Standard Strand 


60 
25 


3-Ply No. 8B.W.G. Twisted Guy 
Wire 


60 
25 


No. 6 B.W.G. "BB" Tel. Wire 


60 
25 


Curves of Effective Resistance and Internal Reactance 
for each of the seven samples, per 1,000 feet of single 
conductor, at 25 and 60 cycles, will be found at the end 
of this report. It should be kept in mind that these 
curves show the characteristics of but one sample in 



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each case and are not average results determined from 
a comprehensive series of tests intended to be complete- 
ly representative of each class or grade as a whole. 
But there is no reason to doubt that each sample, with- 
in reasonable tolerance Umits, is characteristic of its 
class. 

Tables of Effective Resistance, Internal Reactance and 
Ldne Loss for each of the seven samples, per mile of 
conductor, will be found at the end of the report supple- 
menting the curves before mentioned. 

Cofflparisan of Results 

Comparisons Among Three Different Grades of Strand 
of Eqiuil Size. The three strands of ^-in. "High 
Strength", "Siemens-Martin'' and "Standard'' grades 
afford a basis of direct comparison at equal current 
densities, as shown in the next table. 



Comparisofls Ammg Three Different 6rades of %-iii. Steel Strand 




Skin E£fect Renstanoe Ratio 


Internal Inductance Ratio 


Currrent 

in 
Amperes 


High 

strength 

strand 


Sieman»- 
Martin 
Strand 


standard 
strand 


High 
Strength 
Strand 


Siemens- 
Martin 
strand 


Standard 
strand 


60 CYCLES 



5 
10 
15 
20 
25 



1.006 


1.008 


1.080 


13.11 


13.55 


1.007 


1.009 


1.130 


13.75 


14.41 


1.011 


1.011 


1.207 


14.29 


15.26 


1.013 


1.016 


1.346 


14.91 


16.00 


1.016 


1.017 


1.512 


15.59 


16.71 



31.38 
37.98 
45.44 
54.54 
61.23 



25 CYCLES 



5 

10 
15 
20 
25 



1.002 


1.002 


1.036 


13.19 


13.52 


1.001 


1.003 


1.064 


13.80 


14.52 


1.001 


1.004 


1.117 


14.47 


15.33 


1.003 


1.005 


1.191 


15.13 


16.10 


1.005 


1.006 


1.250 


15.92 


16.77 



37.72 
47.64 
59.90 
73.25 
82.70 



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The foregoing comparisons show that the skin-eflFect 
resistance ratios in the "High Strength" and "Siemens- 
Martin" samples are of a nominal order and increase 
but slightly with the current density; the internal in- 
ductance ratios are also of relatively small magnitude 
and consistent with the low values of skih-effect resist- 
ance ratio. These samples evidently have low mag- 
netic permeability characteristic of medium hard steel. 
The sample of "Standard" grade exhibits pronounced 
skin effedt increasing rapidly with increase of current 
density and much higher internal inductance ratios, 
impljring that the steel is considerably softer than the 
other two samples. These results as a whole are con- 
sistent with the respective values of conductivity (D.C.) 
which are approximately 10% of the International An- 
nealed Copper Standard for "High Strength" and 
"Siemens-Martin" and 15% for "Standard". 

Owing to the differences above mentioned, it be- 
comes a question in any practical case as to which 
grade of steel should be selected in order to obtain the 
smallest permissible conductor from the electrical stand- 
point. This will be made clearer by the next table com- 
paring the actual effective resistances of these three 
samples. 



Effective (A. C.) Resistance of %-ifl. 

Per Mile 



Steel Straod — Ohms 



Current 

in 
Amperes 



6 

10 
15 
20 
25 



60 CYCLES 



High 
strength 
strand 



5.871 
5.892 
5.935 
6.977 
6.030 



Siemena- 
Martin 
Strand 



5.444 
5.465 
5.491 
5.549 
5.623 



standard 
Strand 



3.912 
4.071 
4.367 
4.979 
5.634 



25 CYCLES 



High 
strength 
Strand 



5.834 
5.840 
5.861 
5.935 
5.993 



Siemens- 
Martin 
Strand 



5.423 
5.433 
5.470 
5.512 
5.565 



Standard 
Strand 



3.733 

3.844 
4.071 
4.382 
4.620 



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It appears from the comparisons in the last table that 
the "Standard" sample will have lower effective (A.C.) 
resistance at 60 cycles, up to 25 amper^ but for lai^ger 
currents it is probable that the "Siemens-Martin" 
sample will have the lower resistance; at 25 cycles the 
"Standard" sample has in every case lower resistance 
than the "Siemens-Martin", although the two show a 
tendency to approach the same resistance at some lar- 
ger value of ciurent. In every case the internal reac- 
tance of the "Standard" sample is several times larger 
than that of the other two. 

Comparisons Among Three Different Sizes of Siemens-^ 
Martin Strand exhibit fairly consistent results. The 
skin-effect resistance ratio, while nominal in value, in- 
creases slightly with increasing current and also increas- 
es slightly with increasing diameter of strand, but de- 
creases with lower frequency. The internal inductance 
ratio shows a slight but consistent increase with increas- 
ing current; as a whole it also shows a very slight 
increase at the lower frequency and a slight tendency 
to increase with decreasing diameter of strand, which 
corresponds, at the same current value, to increasing 
current density. The main characteristics of these 
three samples of "Siemens-Martin" strand are: (a) 
nominal skin effect; (b) relatively low internal induc- 
tance ratio; (c) neither skin-effect nor inductance ratio 
are very materially affected by changes in frequency 
(below 60 cycles) and current density. 

Comparisons Among Standard Strand, Guy Wire and 
B.B. Wire disclose certain characteristic differences, 
particularly noticeable in the case of the sample last 
mentioned. The comparisons set up in the next table 
are based on equal currents and consequently, because 
of differences in cross-section, do not represent equal 
current densities; for equal values of current the den- 
sity is least in the "Standard Strand", intermediate in 
the "Guy Wire" and highest in the "B.B." wire. 



28 uigitized by '\^jOOQ IC 



INDIANA STEEL AND WIRE COMPANY, MuncU, Ind. 



Conparisoos Ainoog Staiidard Strand, Qay Wire and ''B. B." Wire 



Cuneiit 

in 
Amperes 



Skin Bi7eet Resistanoe Ratio 



H-in. 

Stendard 

Strand 



S-Ply 

No 8 Guy 

Wire 



No. 6 
Wire 



Internal Inductance Ratio 



?f4n. 

Standard 

Strand 



a-Ply 

No. 8 Guy 

Wire 



No. 6 

"B3." 

Wire 



60 CYCLES 



5 

10 
15 
20 
25 



1.080 


1.059 


1.525 


31.38 


31.67 


1.130 


1.102 


1.950 


37.98 


40.11 


1.207 


1.179 


1.990 


45.44 


50.52 


1.346 


1.275 


1.900 


54.54 


62.25 


1.512 • 


1.345 


1.760 


61.23 


71.95 



235.1 
264.7 
270.6 
268.9 
257.1 



28 CYCLES 



6 

10 

15 
20 
25 



1.036 


1.018 


1.281 


87.72 


31.42 


1.064 


1.034 


1.508 


47.64 


40.11 


1.117 


1.073 


1.494 


59.90 


54.24 


1.191 


1.152 


1.433 


73.25 


69.54 


1.250 


1.195 


1.373 


82.70 


86.24 



810.6 
429.9 
437.8 
432.6 
423.1 



The skin-effect resistance ratio, making allowance for 
differences in density at equal values of current, is 
least in the "Guy Wire" and maximum in the "B.B/' 
wire. The same relations hold true for the internal in- 
ductance ratio, thus indicating that the "Guy Wire" 
is the hardest sample of the three, "Standard Strand" 
being intermediate and "B.B." wire the softest. Be- 
sides havine much the highest skin-effect resistance 
ratio of all the samples, the "B.B." wire also has by far 
the largest internal reactance. A further effect noted 
onljr in the "B.B." sample is the decrease of sldn-effect 
resistance ratio and internal inductance ratio after the 
current exceeds approximately 15 amperes, which cor- 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



responds to the characteristic maximum point or hump 
in the flux-permeability curve of soft iron or soft steel. 
Possibly the same effect would be noted in the case of 
the '^ Standard Strand" or the "Guy Wire" sample if 
the current density were increased to considerably 
greater values. 

While there might be some question, in a particular 
case, whether "Guy Wire" or "Standard Strand" 
would be the better choice as between the two, it is 
fairly evident that both are superior to "B.B." wire, at 
least so far as these tests show. By applying skin-effect 
resistance factors to the values of volume resistivity 
given earlier in this report, it will also be seen that 
"B.B." wire at 60 cycles is probably inferior to "Sie- 
mens-Mairtin" steel at equal current densities; at 25 
cycles the reverse is probably true. 

Wave Distortion. In the tests on the smaller wires 
it was noted that wave distortion was produced and 
this was severest with the No. 6 "B.B." sample. The 
reason for such distortion is the varying permeability 
of the steel or iron with changes in current strength 
from instant to instant, which in turn causes correspond- 
ing changes in the instantaneous values of internal induc- 
tance and internal reactance. Such pulsation of the 
internal reactance is sufficient in itself to cause wave 
distortion, but its effect as a whole is augmented by the 
fact that it causes corresponding pulsation of the effec- 
tive (A.C.) resistance. Current of sine-wave shape was 
maintained in each sample throughout the tests, with 
the result that distortion occurred in the potential wave 
of impedance drop across the terminals of the test loop. 
Suitable means were adopted in the tests to eliminate 
the effects of any such distortion upon the results. 

Wave distortion is objectionable per se, because it 
tends to increase the losses in any alternating current 
system and impair the efficiency. While no specific 
investigation of wave distortion has been made in con- 
nection with these tests, it is proper to point out that 



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INDUNA STEEL AND WIRE COMPANY, Muncie, Ind. 



such distortion will always occur in some degree with 
iron and steel conductors, being most pronounced with 
wires of high permeability and vice versa. This consti- 
tutes an objection to the use of that class of alternating 
current conductors of which the No. 6 "B.B." wire is 
generally tvpical, although the objection is not neces- 
sarily conclusive. The corresponding advantage in the 
use of the harder grades of material, such as "Siemens- 
Martin", or "Hieh Strength" is self-evident. With 
the latter materials the skin-effect resistance ratio and 
the internal inductance ratio are both so nominal in 
value that the resultant wave distortion is probably 
insignificant from a commercial standpoint. 

Commercial Applicatioo 

Line Resistance, Reactance and Impedance per 1,000 
feet or per mile of single conductor at 25 or 60 cycles 
with any particular spacing or arrangement of conduc- 
tors may be determined from the data previously giv- 
en, according to well known methods. In order to 
facilitate rapid determination of the total effective re- 
actance, the following rule will sometimes be conven- 
ient for making use of reactance tables for copper con- 
ductors: determine from such a table the reactance of 
a copper conductor of the same size as the steel conduct- 
or under consideration, at the given frequency and 
conductor spacing; subtract from the total reactance 
thus found the internal reactance (given below) and 
add to the remainder the effective internal reactance of 
the steel conductor under the stated conditions as to 
frequency and current density, which will give the total 
reactance desired. When not convenient to make use 
of tables, the total reactance for steel may be found by 
computing the external reactance from the inductance 
formulas previously given and adding to this result the 
proper value of internal reactance for the stated condi- 
tions. The internal reactances of copper conductors in 
ohms per mile, neglecting skin effect, are as follows: 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind. 



Solid Wire 
3-Ply Strand 
7-Wire Cable 



60 CYCLES 



0.030 
0.047 
0.039 



25 CYCLES 



0.013 
0.020 
0.016 



Ldne Drop and Loss are computed by well known 
methods which may be found in various standard text- 
boolffl and handbooks. Particular care should be taken 
in the case of iron and steel conductors, however, to 
use the effective values of resistance and reactance 
which would exist under the stated condition of fre- 
quency and current density. 

Current Carrying Capacity of any conductor is lim- 
ited by that value of Ih- or energy loss which raises its 
temperature to the safe maximum limit. This capac- 
ity being well defined for copper conductors (National 
Electrical Code Rules), it is possible to make an ap- 
proximate rule for iron and steel conductors which will 
m general be a safe guide. The rule may be stated as 
follows: Divide the conductivity (D.C.) ratio of steel 
to copper by the skin-effect resistance ratio, find the 
square root of the result and multiply this figure by the 
current-carrying capacity of a copper conductor of the 
same size as the steel conductor under consideration, 
which will give the desired approximate carrying capac- 
ity of the steel conductor. Example: the conductiv- 
ity ratio of a certain No. 6 B. W. G. steel wire is 10 per 
cent and its skin-effect resistance ratio at about 25 amp. 
is 1.12; the quotient of 0.100^1.12 is 0.0893 and the 
square root of 0.0893 is 0.299; the nearest A. W. G. 
size of copper wire is No. 4, which has a carrying capac- 
ity of 90 amp.; the product of 90x0.299 is substan- 
tially 27 amp., which is the approximate canying 
capacity of this No. 6 steel wire for the same tempera- 
ture rise permissible with copper wire of equal size. 

Example of Applicability of Steel Cable to High-Ten- 
don Transmission. Given a 20-mile, 3-phase, 110,000 



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INDUNA STEEL AND WIRE COMPANY, Munde, Ind. 



volt, 60 cycle line delivering 5,000 kva at 80% power 
factor, with permissible line drop not exceeding 10% 
and a conductor spacing of 10 ft. Consideration of the 
factor of corona discharge at once fixes the minimum 
permissible cable diameter at approximately 0.43 in., 
provided the line is situated at sea level and the tem- 
perature does not exceed 25 deg. Cent, or 77deg. Fahr. 
Let it be assumed that because of elevation and tem- 
perature a 0.5-in. cable must be used. As a first approxi- 
mation assume that the line drop will be the fidl 10% 
allowed; it follows that the load current at the receiver 
will be 29.2 amp. per phase wire. A 0.5-in. Siemens- 
Martin cable, at 25 amp., will have an eflfective resist- 
ance of 3.47 ohms per mile and an internal reactance 
of 0.614 ohm per mile; the external reactance will be 
0.749 ohm, making a total reactance of 1.36 ohms per 
mile. Taking slightly higher values of resistance and 
reactance, say 3.5 ohms and 1.40 ohms respectively, 
and computing the total line drop upon the assumption 
that the Une charging current can be neglected, it ap- 
pears that the drop will be approximately 3%. The 
line charging ciurent, computed upon the assumption 
of constant line pressure from end to end, will be 6.9 
amp. per phase wire, or roughly one-fourth of the load 
current. It is evident without further consideration 
that the 0.5-in. Siemens-Martin cable will more than 
satisfy the requirements as to voltage regulation. 

Second Example. Given a 10-mile, 3-phase, 33,000 
volt, 60 cycle fine delivering 500 kva at 85% power 
factor, with a line loss not exceeding 10% of the power 
delivered to the line; conductor spacing, 36 in. De- 
livery of 500 kva at 33,000 volts will require approxi- 
mately 8.8 amp. per phase wire, but on account of the 
line drop, which will reduce the voltage at the receiver, 
it may be assiuned that the actual current will be about 
9.5 amp. The delivered energy is 425 kw, representing 
90% of the total energy delivered to the line, and there- 
fore the permissible total line loss is 47.2 kw, or 1.57 kw 
per mile of wire. Dividing the line loss per mile by the 
square of the assiuned current gives a Une resistance of 



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INDIANA STEEL AND WIRE COBfPANY, Muneie, Ind. 



approximately 17 ohms per mile. The constants for 
0.25-in. Siemens-Martin cable at 60 cycles, 10 amp., 
are 12.38 ohms resistance and 0.577 ohm internal reac- 
tance per mile; the external reactance is 0.687 ohm per 
mile, making a total of 1.264 ohms per mile. Assuming 
6% drop (2,000 volts, delta) or a delivered voltage of 
31,000 at the receiver, and recalculating the problem, 
the line loss is found to be approximately 7.1% and the 
drop 5.6%. This calculation neglects the effect of the 
line charging current, which would be approximately 
1.1 amp. per phase wire or but 12% of the load current, 
bringing the Une loss up to possibly 8%. If a hard- 
drawn copper conductor were used for this line, con- 
siderations of voltage and tensile strength would require 
No. 4 A. W. G., which would have practically the same 
weight as the 0.25-in. Siemens-Martin cable but only 
two-thirds the strength. 

Example of Applicability to Short Ldnes Carrying SmaU 
Loads. Given a 5-mile, 3-phase, 6,600 volt, 60 cycle line 
delivering 100 kw at 80% power factor with not more 
than 10% loss; conductor spacing, 24 in. As a first 
approximation, the limiting line resistance may be com- 
puted upon the basis of 8% drop. At the latter value of 
drop, the current necessary to deliver the load will be 
approximately 12 amp. The total permissible line loss is 
one-ninth of 100 kw or 11.1 kw. Dividing the last figure 
by the square of the line current gives a total effective 
resistance of 77.1 ohms or 5.14 ohms per mile. The 
conductor of nearest resistance is 0.375-in. Standard 
Strand. By interpolation, it will be found that this 
strand, at 12 amp., has an effective resistance of 4.17 
ohms per mile and an effective internal reactance of 
1.59 ohms per mile. The external reactance is 0.56 ohm 
per mile, making a total reactance of 2.15 ohms per mile, 
recalculating the problem on this basis shows that the 
line loss will be 8.1% of the energy delivered to the line 
and the drop will be 7.4% of the impressed voltage, 
which come within the requirements. If this line should 
be erected at first with only two conductors (instead of 
three) and operated single-phase, it would deliver one- 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind. 



half as much energy, or 60 kw at 80% power factor, 
with the same percentage of loss and drop. 

Relative Costs of steel conductors in comparison with 
copper or any other material mav be computed with 
fair precision for any given set of conditions, but the 
variables are so numerous that general comparisons 
are difficult. The basis of comparison should be the 
total annual charges in each case, including interest, 
taxes, depreciation, repairs and the annual cost of sup- 
plying the line losses. Depreciation is the only factor 
which is open to any substantial degree of uncertainty, 
and is usually based upon some assiunption as to useful 
life which seems reasonable under the circumstances of 
a specific case. The life of galvanized iron and steel 
conductors is greatly dependent upon the local atmos- 
pheric conditions, ranging anywhere from a few years 
m sulphurous or fog-laden atmospheres to 20 to 25 
years in regions of comparatively dry climate and pure 
atmosphere. A reasonable assumption under condi- 
tions which do not represent either extreme is probably 
15 years. 

Conclusions. In selecting steel conductors for alter- 
nating-current transmission or distribution lines the 
choice of the harder grades of material will insure 
minimum skin-effect and internal reactance and 
maximum tensile strength. The characteristic condi- 
tions under which steel power conductors may be used 
with advantage can be siunmarized as follows: 

(a) For lines of short or moderate length at very high 
tension, where the minimum size of conductor is 
fixed by corona discharge and the line resistance 
is a secondary consideration. 

(b) For high-tension lines of short or medium length 
transmitting moderate amounts of energy, such 
that the line drop and the line loss fall within per- 
missible limits, as for example in the case of branch 
or tap lines of high-tension networks. 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Jnd. 



(c) For short lines delivering small amounts of energy 
at the primary voltages customary in urban and 
rural distribution, such that the drop and the loss 
are not excessive. 

(d) For long or unusually severe spans requiring 
greater tensile strength and factor of safety than 
can be obtained with copper or aluminum. 

Respectfully submitted, 



Consulting Engineer 



Chicago, 111. 
March 1, 1921 



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APPENDIX A. 

CURVES OF EFFECTIVE RESISTANCE 
AND INTERNAL INDUCTANCE 



NOTE: These curvet were plotted from the data 
given in the main body of the report, for each 
■ample of conductor subjected to test. 



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INDIANA STBEL AND WIRB COMPANY, Muneie, Ind. 



APPENDIX B. 

TABLES OF EFFECTIVE RESISTANCE, 
INTERNAL REACTANCE AND LINE LOSS 



NOTE: TheM tables were prepared from the data 
given in the main body of the report, for each 
■ample of conductor subjected to test. 



63 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind. 


Resistaice, tatenud Reactaace and Liae Loss of wia. 
Bigh Streagth Straad 


Current 

in 
Ampem 


60 CYCLES 


28 CYCLES 


Ohnui per Mile 


lineLoM 
in Watts 
per Mile 


Ohms per Mile | 


lineLoM 


Radttanoe 


Internal 
Reactance 


Resistanoe 


Internal 
Reactance 


per Mile 


5 
10 
16 
20 
26 


5.871 
5.892 
6.935 
6.977 
6.030 


0.511 
0.535 

0.567 
0.681 
0.607 


146.8 
589.2 

1336. 

2391. 

3769. 


5.834 
5.840 
5.861 
5.935 
6.993 


0.214 
0.224 
0.235 
0.246 
0.258 


145.9 

584.0 
1319. 
2374. 
3746. 


Resistance, tateroal Reactance and Line Loss of i^-in. 
Siemens-Martia Strand 


Cuxrent 

in 
Ampem 


60 CYCLES 


25 CYCLES 


Ohma per MUe 


LineLoM 

in Watts 
per Mile 


Ohms per Mile 


lineLoM 


Reaistanoe 


Internal 
Reactance 


Resistonce 


Internal 
Reactance 


in Watts 
per Mile 


5 
10 
16 
20 
26 


3.400 
3.421 
3.427 
3.443 
3.474 


0.536 
0.658 
0.574 
0.689 
0.614 


85.0 

342.1 
771.1 

1377. 

2171. 


3.374 
3.379 
3.390 
3.400 
3.411 


0.231 
0.235 
0.244 
0.262 
0.261 


84.4 
337.9 
762.8 

1360. 

2132. 





55 



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INDIANA STRET- AND WIRE COMPANY, Munde, Ind. 


Resistance, Internal Reactance, and Line Loss of %-in. 




Siemens-Nartiii Straod. 


Current 

in 
Amperes 


60 CYCLES 


25 CYCLES 1 


Olims per Mile 


Line Loss 
in Watts 
per Mile 


Ohms per MUe 


LineT^oss 
in Watts 
per Mile 


Resistance 


Internal 
Reactance 


Resistance 


Internal 
Reactance 


5 


5.444 


0.528 


136.1 


5.423 


0.220 


135.6 


10 


5.465 


0.561 


546.5 


5.433 


0.236 


543.3 


15 


5.491 


0.594 


1235. 


5.470 


0.249 


1231. 


20 


5.549 


0.623 


2220. 


5.512 


0.261 


2205. 


25 


5.623 


0.651 


3514. 


5.565 


0.272 


3478. 


1 


Resbtaoce, Internal Reactance and Line Loss of VA-in. 




Siemens-Martin Strand. 


Current 

in 
Amperes 


60 CYCLES 


28 CYCLES 


Ohms per Mile 


lineT^OM 
in Watts 
per Mile 


Ohms per Mile 


Line Loss 
in Watts 
per Mile 


Resistance 


Internal 
Reactance 


Resistance 


Internal 
Reactance 


5 


12.25 


0.551 


306.3 ' 12.20 


0.231 


305.0 


10 


12.38 


0.577 


1238. 


12.30 


0.242 


1230. 


15 


12.54 


0.621 


2822. 


12.61 


0.258 


2815. 


20 


12.75 


0.649 


5X00. 12.72 


0.272 


5088. 


25 


13.04 


0.698 


8150. 1 13.02 


0.295 


8138. 





56 



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INDIANA STE3EL AND WIRE COMPANY, Muncie, Ind. 


Resistance, bteraal Reactance and Line Loss of %-in. 
Standard Strand 


Current 

in 
Amperes 


60 CYCLES 1 


25 CYCLES 


Ohms per Mile 


line Loss 

in Watts 
per Mile 


Ohms per Mile 


line Loss 
in Watts 
per Mile 


Resistance 


Internal 
Reactance 


Resistance 


Internal 
Reactance 


5 
10 
15 
20 
26 


3.912 
4.071 
4.367 
4.979 
5.634 


1.222 
1.479 
1.770 
2.124 
2.386 


97.8 
407.1 
982.6 

1992. 

3521. 


3.733 
3.844 
4.071 
4.382 
4.620 


0.612 

0.773 
0.972 
1.189 
1.342 


93.8 
384.4 
916.0 
1768. 

2887. 


Resistance, Internal Reactance and Line Loss of 3-Pij 
No. 8 Twisted Qnj Wire 


Current 

in 
Amperes 


60 CYCLES 


25 CYCLES 


Ohms per Mile 


Line Loss 
in Watts 
perBiile 


Ohms per Mile 


Line Loss 
in Watts 
perMOe 


Resistance 


Internal 
Reactance 


Resistance 


Internal 
Reactance 


5 

10 
15 
20 
25 


5.734 
5.987 
6.426 
7.091 
7.677 


1.496 

1.893 
2.385 
2.938 
3.396 


143.4 
598.7 

1446. 

2836. 

4736. 


5.512 
5.613 
5.887 
6.362 
6.706 


0.618 
0.789 
1.067 
1.368 
1.697 


137.8 
561.3 

1325. 

2545. 

4191. 





57 



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INDIANA STEEL AND WIRE COMPANY, Muneie, Ind. 



Resistance, Interoal Reactance and Line Loss of Ho. i 
H H Telegraph Wire 



Current 

in 
Amperes 



6 
10 
16 
20 
25 



60 CYCLES 



Ohms per Mile 



Reeistanoe 



13.41 
17.21 
17.82 
17.66 
17.00 



Internal 
Reactance 



7.187 
8.081 
8.212 
8.162 
7.805 



lineLoee 
in Watts 
per Mile 



335.3 

1721. 

4010. 

7024. 

10630. 



25 CYCLES 



Ohms per Mile 



11.80 

13.46 
13.67 
13.28 
13.17 



Internal 
Reactance 



3.928 
6.437 
6.636 
6.470 
5.851 



Line Lobs 
in Watte 
per Mile 



282.5 

1346. 
3053. 
6312. 
8283. 



lOogle 



58 



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INDIANA STEEL AND WIRE COMPANY, MuneU, Ind. 



APPENDIX C. 

TELEPHONE TRANSMISSION 
EQUIVALENTS OF IRON WIRE 



NOTE: Th« authority for the following data, hare 
given for convenience, is the ''Standard Handbook 
For Electrical Engineera," Fourth Edition. 



59 



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INDIANA STEEL AND WIRE COMPANY, Muncie, Ind, 



Appendix C. 
Telephone Transmissioa Eqaiyaleiits of Iron Wire 

For convenience in connection with private telephone 
lines frequently carried on the same structures with 
transmission and distribution lines, the following aver- 
age values of telephone transmission equivalents of iron 
wire are appended. These equivalents apply to iron 
wire of "B. B/' quality when new. Transmission nat- 
urally becomes impaired as corrosion takes place and 
reduces the cross-section. Such corrosive action fre- 

Siently makes its first appearance at the joints and for 
is reason the joints in u*on wire should always be care- 
fully soldered when the line is erected. Transmission 
equal to 80 miles of No. 19 standard cable will as a rule 
be quite satisfactory for private line service, assuming 
that the stations situated adjacent to sources of ex- 
traneous noise, as in power stations or sub-stations, are 
properly housed in sound-proof booths. 



Material 



Copper 
B.B. Iron 
B.B. Iron 
B.B. Iron 
B. B. Iron 



Gage 



No. 9 A.W.G. 
No. 8 B.W.G. 
No.lOB.W.G. 
No. 12 B.W.G. 
No. 14 B.W.G. 



Diameter 

(in.) 



0.1144 
0.1650 
0.1340 
0.1090 
0.0830 



Miles Eouivalent 

to one Mile of 

No. 19 Standard 

Cable 



15.6 
4.5 
4.0 
3.1 
2.5 



Miles Equivalent 

to 80 Miles of 

No. 19 standard 

Cable 



470. 
135. 
120. 

98. 

75. 



61 



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